Flexographic printing plate precursors having a laser-ablatable mask layer on its surface are known in the art. A relief image can be produced in such precursors without the use of a digital negative image or other imaged element or masking device. Films with a laser-ablatable mask layer can be formed by first imagewise exposing the film with laser radiation (generally an infrared radiation laser under computer control) to selectively remove the mask layer in the exposed areas. The mask-containing film is then placed in contact with a radiation-sensitive flexographic printing plate precursor and subjected to overall exposure with actinic radiation (for example, UV radiation) to cure the precursor in the unmasked areas and thus form a negative image of the mask in the precursor. The non-exposed regions of the precursor are then removed using a suitable organic solvent developer to provide a relief image where curing took place. After drying, the resulting relief image is useful in a flexographic printing plate.
An important advance in the art of making and using masking films is described in U.S. Patent Application Publication 2005/0227182 (Ali et al., herein cited as US '182). The described method provides a mask image in significantly less time due to greater imaging sensitivity. In some embodiments, a mask image is formed in a film that includes a carrier sheet and a release layer. The film with the mask image is brought into contact with a flexographic printing plate precursor that is then imaged through the mask image. The film with the mask image can be peeled off the release layer prior to development of the imaged precursor. Also, with the use of patterns as described in U.S. Patent Application 2010/0143841 (Stolt et al.), the peel force can be excessive due to the amount of contact edges in the imaged film.
U.S. Pat. No. 7,802,598 (Zwadlo et al.) describes a lamination device that can be used to prepare flexographic printing plates in which a film with a mask image is laminated with a flexographic printing plate precursor prior to imaging. The device is used to apply optimal force to ensure optical contact while minimizing lateral film distortion.
U.S. Pat. No. 7,279,254 (Zwadlo) describes a method for preparing relief images in flexographic printing plates using a removable imaged film containing a mask image. This imaged film is laminated or otherwise brought into optical contact with a flexographic printing plate precursor that includes a photosensitive material and a transparent releasing layer that is composed of, for example, a polyamide. The photosensitive material is exposed to curing radiation through the mask image and the imaged film is peeled off at the release layer. The imaged precursor is then developed to remove non-exposed regions as well as the release layer to form the desired relief image.
There remains a need to improve the methods of making flexographic printing plates using a release layer between the imaged film and flexographic printing plate precursor the flexographic printing plate assembly. Sometimes peeling off the imaged film leaves residual material from that imaged film on the imaged precursor and this inhibits its development. To minimize this problem, peeling should be done very slowly while the flexographic printing plate assembly is held down. Obviously, this lengthens the time for providing the desired relief image. There is a need for a more efficient process for providing flexographic printing plates.